1. Field of the Invention
The present invention relates to a multiband satellite antenna; more particularly, the present invention relates to a multiband satellite antenna for receiving satellite signals.
2. Description of the Related Art
Recently, as the space technology advances, the applications of satellite bring more and more convenience into people's life. Satellites are widely applied in various technologies including, for example, explorations, weather forecasting, or global positioning, etc., and especially mature in signal transmissions. Satellites are used as a transmitting medium for signal transmissions in communication, data transmission, or video/audio broadcasting fields. However, as the demand of applying satellites to signal transmissions grows, the number of satellites and the available frequency bands should be increased accordingly.
In general, the common frequency bands for satellite communications include Ku frequency bands and Ka frequency bands. The Ka frequency band has a higher frequency and is less affected by terrestrial microwaves but seriously affected by rainfalls. The Ku frequency band has a lower frequency and is more affected by terrestrial microwaves but less affected by rainfalls. Current satellites include a wideband satellite, which can transmit signals of the two frequency bands simultaneously, and therefore, a corresponding antenna should have the ability to receive signals of the two frequency bands simultaneously. As shown in FIG. 1A, a traditional dual-frequency satellite antenna includes a wave receiving device 5, which has a Ka band wave guide 10 and a Ku band wave guide 20 disposed coaxially. The Ku band wave guide 20 has a larger inner diameter and surrounds the Ka band wave guide 10. A high frequency suppression module 30 is disposed outside the Ku band wave guide 20 for suppressing the high level mode in electric fields, so that the field pattern produced by the wave receiving device 5 can be smoother and more symmetrical. However, since the Ku band wave guide 20 is disposed coaxial with the Ka band wave guide 10, the inner diameter of Ku band wave guide 20 should be increased to correspond to the Ku frequency band. Therefore, the wave receiving device 5 has a larger volume according to this design.
In addition, taking geosynchronous satellites as an example, because the number of satellites keeps increasing while orbit positions are limited (360 degrees), consequently, the International Telecommunication Union (ITU) have changed the satellite distribution from every 3 degrees to every 2 degrees for one satellite. Due to the decrease in the included angle between satellites, the wave receiving device needs to be adjusted accordingly. FIG. 1B illustrates a traditional wave receiving device 7 capable of receiving signals from several satellites simultaneously. The wave receiving device 7 includes a Ku band wave guide 20 in the middle and Ka band wave guides 10 on two sides. In such a design, the satellite signals received at a same elevation angle are single frequency signals, and therefore, the wave receiving device 7 is not applicable to dual frequency satellite signals. Furthermore, in such a design, the space between the two Ka band wave guides 10 is limited, and therefore, only one Ku band wave guide 20 can be accommodated therein. Additionally, because the space between the two Ka band wave guides 10 is limited, the wave receiving device 5 of FIG. 1A cannot be disposed therein.